The present invention relates in general to multi-band electromagnetic wave detectors and, more particularly, to radar detectors and methods of operating radar detectors that identify and/or inhibit detected in-band signals that are not of interest, e.g., signals that are transmitted by other radar detectors.
Police and other authorities use radar waves to monitor the speed of various objects, including the speed of motor vehicles. Such radar devices are typically operated in one of four frequency ranges or bands, including the X band, which spans the range of 10.50 gigahertz (GHz) to 10.55 GHz, the Ku band, which spans the range of 13.40 GHz to 13.50 GHz, the K band, which spans the range of 24.05 GHz to 24.25 GHz and the Ka band, which spans the range of 33.4 GHz to 36.0 GHz. Electromagnetic signals within the above bands may thus be monitored to alert a motorist of the presence of radar devices.
A conventional radar detector comprises a superheterodyne radio receiver that includes generally, an antenna, a mixer and a detector. The mixer combines the electromagnetic signals received by the antenna with a local oscillator signal that is repeatedly swept to scan one or more of the X, Ku, K and Ka bands to convert the frequency of the received signals in the swept bands to a predetermined intermediate frequency at the mixer output. The detector circuitry analyzes the signals from the mixer output, which have been converted to the intermediate frequency, to determine whether in-band radar signals are present.
In practice, the local oscillator signal may be derived from any one of two or more local oscillators that are switched in a time-sharing sequence according to the particular band being scanned. For example, a first local oscillator may be swept for detection of the X and K bands, a second local oscillator may be swept for the detection of the lower portion of the Ka band and a third local oscillator may be swept for the detection of the upper portion of the Ka band. Due to the location of the local oscillators, their corresponding mixer and antenna, conventional radar detectors leak electromagnetic waves corresponding to the fundamental frequency of the local oscillators and their corresponding harmonic spectra via the antenna.
Accordingly, when operating a radar detector in the vicinity of one or more other radar detectors, it is possible that a first detected signal that is in the harmonic spectra of an electromagnetic wave leaked by a nearby detector will be falsely recognized as a radar signal if the first detected signal is contained in a radar band being scanned. This phenomenon is particularly prevalent when scanning the Ka band as either the second harmonic or the third harmonic of many leaky local oscillator frequencies falls within the Ka band.